Well centralizer

ABSTRACT

The centralizer consists of axially-spaced collars connected usually by groups of bowed leaf springs for slidable reception upon a casing or other pipe extending into a well. At least one group of springs is for engaging the surrounding well wall, while the other springs, which may be prestressed or of different resistance to flexing, serve, primarily, to increase the bending resistance of the first group of springs.

United States Patent 1 Hall, Sr.

[ WELL CENTRALIZER [75] inventor: John A. Hall, Sr., Weatherford, Tex.

[73] Assignee: Weatherford Oil Tool Company,

Houston, Tex.

[22] Filed: Oct. 13, 1972 [21] Appl. No.: 297,224

Related US. Application Data [63] Continuation of Ser. No. 688,188, Dec. 5, 1967, abandoned, which is a continuation-in-part of Ser. No. 577,364, Sept. 6, 1966, Pat. No. 3,643,739.

g 1 565 "x. l i 4 l 1 July 31, 1973 1,835,377 12/1931 Clark et a1. 166/241 X 2,482,985 9/1949 Lockwood 166/241 2,605,844 8/1952 Clark 166/241 2,636,564 4/1953 Kluck 166/241 2,656,890 10/1953 Brandon 166/241 3,270,697 9/1966 Solum 166/241 X Primary ExaminerDavid H. Brown Attorney-Bertram l-l. Mann et a1.

[5 7 ABSTRACT The centralizer consists of axially-spaced collars connected usually by groups of bowed leaf springs for slidable reception upon a casing or other pipe extending into a well. At least one group of springs is for engaging the surrounding well wall, while the other springs, which may be prestressed or of different resistance to flexing, serve, primarily, to increase the bending resistance of the first group of springs.

13 Claims, 12 Drawing Figures Patented July 31, 1973 3,749,168

4 Sheets-Sheet I J J Jofin ,4. //a'//, j,- INVENTOR.

ATTORNEY Patented July 31, 1973 4 Sheets-Sheet 2 (/5/7/7 A. flc7//,Jr

INVENTOR.

ATTORNEY Patented July 31, 1973 3,749,168

4 Sheets-Sheet L5 ATTORNEY Patented July 31, 1973 4 Sheets-Sheet 4.

IN VEN TOR.

BYb/j;yg /W WELL CENTRALIZER CROSS REFERENCES TO RELATED APPLICATIONS This application is a continuation of my copending U.S. Pat. application Ser. No. 688,188 filed Dec. 5, 1967, which now abandoned was a continuation-inpart of my US. Pat. application Ser. No. 577,364 filed Sept. 6, 1966, now U. S. Pat. No, 3,643,739.

BACKGROUND OF THE INVENTION l. FIELD OF THE INVENTION The invention relates to centralizers for properly spacing from a wall of a bore hole in the earth, as a well or other cavity or orifice, a pipe or other elongated member extending into the orifice.

2. PRIOR ART In order that a fairly uniform cement sheath may be provided between the casing in an oil well or the like and the bore hole wall, it is desirable to maintain the casing at a substantially uniform distance from the hole wall, and this is usually achieved by means of centralizers which are mounted on the casing. A conventional centralizer of the type now in general use consists of a pair of collars received about the casing and connected by longitudinal or helically inclined, outwardly bowed leaf straps, bars, or wires. The collars may be slidable on the casing, at least to a limited extent, to permit reciprocation and/or rotation of the casing together with scratchers or wipers secured thereto for conditioning the bore wall prior to cementing.

A difficulty with presently-known types of centralizers is that their initial radial resistance may be so small that, particularly in the case of deviated (non-straight) holes, the casing may be permitted to too closely approach the hole wall.

SUMMARY OF THE INVENTION Consequently, an object of the present invention is to provide improved means for controlling, particularly increasing, the lateral resistance to bending of the bowed springs in the above type of centralizer.

Another object is to provide means for increasing the radial resilience of the centralizer without the use of stiffer, thicker, or wider bow springs.

In accordance with the present invention, one or more of the bars connecting the spaced collars of the centralizer is of greater resistance to longitudinal and- /or radial stressing than others whereby effective resistance of the centralizer to radial distortion is varied relative to conventional centralizers, and, specifically, the bows which engage the bore wall are reinforced or rendered more resistant to lateral distortion.

BRIEF DESCRIPTION OF THE DRAWINGS The above objects and others hereafter appearing are attained substantially by the structures illustrated in the accompanying drawings, in which:

FIG. 1 is a half elevation and half longitudinal central section of a length of well casing extending into a well bore and provided with one form of the invention.

FIG. 2 is an enlarged perspective view of a detail showing the means for mounting superposed springs on underlying springs.

FIG. 3 is an end view of the device in FIG. 1 taken substantially on line 3-3 thereof.

FIG. 4 is a view similar to FIG. 3 showing a modification.

FIG. 5 is a half elevation of a length of casing having another modified contralizer thereon.

FIG. 6 is an exploded half elevation of the structure in FIG. 5 and illustrating a method of assembling the same.

FIG. 7 is an end view of another modification.

FIG. 8 is a half elevation of another modification, parts being broken away to better illustrate the underlying structure.

FIGS. 9, 10, 11, and 12 are schematic elevations illustrating other arrangements for prestressing and/or otherwise strengthening the centralizer bows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The form in FIGS. 1 3 includes a plurality of coaxial collars 8, 9, l0, and 11 adapted to be received about a casing section 112 and which comprise the cylindrical body structure of the device. The casing is run into a large size bore hole or shaft 13 having a cavity 14 in one side, in this instance, a key slot. Each adjacent'pair of collars is bridged by an annular series of outwardlybowed straps or leaf springs as 15, 16, and 17, the ends of which are welded to the collars, but may be otherwise secured thereto. Each of the innermost or base straps or springs 15, 16, and 17 is arranged longitudinally and, preferably, one spring in each annular series is longitudinally aligned with corresponding springs in adjacent series to form, in effect, a vertical row. As shown in FIG. 3, eight such longitudinal rows are pro vided around the body structure, although any convenient number may be provided, preferably symmetrically. Also, one end of each of the springs 15, 16, and 17 may be slidable upon its mounting collar.

Mounted upon each adjacent pair in a longitudinal row of the springs or straps 15, 16, and 17 is an intermediate leaf spring, as 18 and 19, the. ends of each latter spring being mounted intermediately on the underlying springs. Secured to the ends of the intermediate springs, as by welding, are clamping brackets, as 20, 21, and 22, one of these being shown enlarged in FIG. 2. The legs of these brackets are folded, as at 23, under and against the centers of underlying springs. Stop lugs 24 and 25 are welded to the end underlying springs 15 and 17 immediately inwardly of brackets 20 and 22. Central bracket 21, which embraces the adjacent ends of both intermediate springs 18 and 19, may be welded, also, to support spring 16. Conveniently, intermediate springs 18, 19 are held initially under slight tension by stop lugs 24 and 25.

Mounted upon each longitudinal pair of intermediate bow springs 18 and 19 is a third annular series of spring straps 28 which centrally engage portions 13 and 14 of the bore wall. Right-hand spring strap 28 in FIG. I is shown as extending into a cavity, as of the key seat type, while the left-hand outermost spring is shown as engaging a portion 13 of the bore wall 13 of normal diameter so as to substantially flatten this spring and cause clamping brackets 29 and 30, folded about intermediate leaf springs 18 and 19, to separate from stop lugs 31 and 32. The corresponding intermediate springs 18 and 19, which cooperate to support outermost spring 28, are flattened to a lesser extent, while the innermost leaft springs 15, 16, and 17 are only slightly flattened if at all. In fact, it is contemplated that the resilience of the successive stacked rows of leaf springs may be decreased outwardly so as to bear more lightly against the bore hole wall, yet be free to flex into cavities.

In the form in FIG. 4, longitudinally rigid bars 34, solid or semicylindrical or of other section, are substituted for the innermost leaf springs I5, 16, and 17 in the first form, while intermediate springs 35 and outermost springs 36 are superimposed thereon in radial stacking.

FIG. 1 also shows a pair of stop collars 38 and 39 of any suitable form secured to the casing or pipe 12 between the end-most collars 8 and 9 and 10 and 11. The vertical rows of stacked leaf springs provided segmental channels or troughs 41 therebetween (FIG. 3) through which are extended pipes 42, for instance, for delivering cement slurry to the well annulus or for other purpose. These rows of springs serve to guide the piping downwardly into the bore hole, such guiding being effective even in the vicinity of substantial cavities, as at 14, which previous centralizers have not been able to reach.

In order to prevent channeling of the cement flowing upwardly along the centralizers and to cause the cement to fill the spaces about the centralizers, guiding or diverting fins may be attached to any number of the bowed springs, as at 43, 44, and 45. One of these is shown enlarged in FIG. 2. The fins are secured by suitable means to the straps and project sidewardly of the straps and are of suitable size and shape to catch and divert the upflowing cement through the loops formed between the springs and/or selectively against the easing and the bore wall. The laterally projecting edges of the fins, preferably, should be curved to prevent catching of pipes being run into the annulus about the casing and centralizers. While only a few of the springs are shown in FIG. I as being equipped with the fins, the fins may be otherwise placed and disposed as desired.

The centralizer, of radially stacked spring elements, may be especially made up to match a particular hole size, although with proper tools the assembly could be achieved wholly or in part in the field. Other stacking arrangements may be utilized, as, for instance, the stacking of intermediate and outer springs upon a single base or inner spring, and the device may be extended laterally as needed by further stacking or reduced by elimination of the outermost springs. In some cases, it may be comvenient to build the device on several conventional centralizers, as heretofore referred to. By laterally extending the centralizer by means of stacked spring elements as herein disclosed and claimed, the unit may be made sufficiently light and compact to be handled by installation workers and will not be too long to be mounted singly or in multiples on a single casing section. While the longitudinal alignment of the tacked springs provides channels for running and segregation of supply pipes, as at 42, the springs may be helically disposed.

In case increased radial rigidity is desired, both ends of all of the bows, or of a part thereof, may be nonmovably secured to the underlying supporting structure. This will have the effect of accumulating the radial resistance of the bow assembly so as to more strongly resist approach of the pipe and bore walls. Furthermore, one or more of the bow springs may be prestressed or otherwise adapted for reinforcing the remaining springs, as suggested in FIGS. 6 l2.

The modified centralizer of FIGS. 5 and 6 comprises a pair of axially spaced collars 50 and 51 slidably received about a casing 52 which extends into a bore hole having the wall 58. The collars are of the split type secured about the casing by means of pin and eye hinges 53 and 54. A stop collar 55 is interposed between the collars to limit reciprocation thereof. The collars are secured together by radially aligned or stacked pairs of bowed spring straps 56 and 57, 56a and 57a, and 56b and 57b, preferably but not necessarily symmetrically disposed about the casing. The ends of the bow springs are welded or otherwise secured together and to the collars, as at 61, and the central portions of the bows are radially spaced. If desired, blocks, as at 64, of rigid or resilient material may be interposed between the spaced central portions of the pairs of bow springs, and the blocks may be secured to one or both of the bows of each pair.

FIGS. 9 and 10 show other modifications of this concept. In FIG. 9, the intermediate portions of bars 56c and 57c are radially spaced and spacer blocks, as 64a, only partially span the radial clearance between pairs of bows. The blocks 640 do not take effect until outer bows 56c have been radially distorted a certain amount. In FIG. 10, filler 64b of rigid material, as cement, or resilient material, as plastic or rubber, fills substantially the entire space between each pair of bows, but may fill only a part of the space. The fillers may be secured to one or both of the abutting pairs to exert different effects. Since the outer bow springs in FIGS. 5, 6, and 8 1 l are of greater radial expanse than the inner springs, only the outer springs or straps are stressed laterally by direct engagement with the bore wall, while the inner bows or straps, subjected to longitudinal stressing only, serve to resist axial separation of collars 50 and 51 and thereby tending to increase the lateral resilience of the outer straps that is, increase their resistance to bending. The effect of this is that the initial radial resilience of the centralizer, tending to resist approach of the casing to the bore wall, is increased without the use of heavier or stiffer bow strap material. The resistance to axial separation of the collars increases as inner straps 57 are reduced in curvature that is, approach a straight line which limit form, of course, would provide maximum resistance to elongation. On the other hand, the resistance to bending of the outer bows due to central application of radial force, as in contacting the bore wall (arrow 62, FIG. 5 is increased as the curvature of the bows is increased. Thus, it is possible for the centralizer manufacturer to achieve a variety of radial resilience characteristics to conform with requirements of customers by varying the curvatures and lengths of the bow straps, particularly the inner straps.

A method of increasing the radial resilience of the centralizer of FIG. 5 is illustrated in FIG. 6. Here, collars 50 and 51 are intitially connected by inner bow springs 57, etc., as in FIG. 1. However, prior to application of outer bow springs 56, the inner springs are radially compressed, as by means of split clamp 60 which is tightened about the central portions of the inner straps. After a predetermined radial compression of the inner straps, outer straps 56 are applied and rigidly secured to the ends of the inner straps and/or the collars, as in FIG. 1. Upon release and removal of stressing clamp 60, the inner bows tend to resume their unstressed shape and to draw together end collars 50 and 51. This action is resisted by the outer bows which are, accordingly, themselves placed and held under initial bending stress. Thus, the radial resistance of the centralizer is increased due to the prestressing of the bow straps. A similar effect could be produced by forcing collars 50 and 51 together to initially shorten the inner straps.

Still another method of prestressing the bow straps is illustrated in FIG. 11 in which the inner straps 57d are secured to collars 50 and 51 as before. Outer straps 56d, being straight members with angled ends 56x and 56y, are then secured at one end to collar 51 upon or adjacent the corresponding end of inner straps 57d. The opposite ends of the outer straps are then bent to the form shown in dot-dash lines at 562 and secured to the underlying straps or collar. Of course, the bending of the outer straps 56d cannot exceed the elastic limit of the metal to preserve initial bending prestress. The reinforcing capacity of the inner springs is accentuated where these springs are shorter in length and/or of lesser curvature than the outer springs.

In FIG. 7, three groups of differently shaped bowed springs 65, 66, and 67 connect the collars. All of these may be of approximately the same length, but of different curvature and radial expanse, as shown, so as to exert different resistances to separation of the collars, as when the outer bows bear against a bore wall. The purpose of the different bows, again, is to provide a specific resistance to radial compression of the centralizer. Different combinations of such bow springs may be provided to achieve different resistance characteristics. For instance, the radial expanse of all bows may be the same, as may be achieved by interposing spacer blocks between the collars and bars 66 and 67, or even mounting a block at the center of such bars, as at 64a in FIG. 9.

FIG. 12 shows a pair of centralizer bars 56e and 572 which may or may not be radially aligned. Here, bars 57e, though shorter than bars S6e, have substantially the same radial expanse and, therefore, different curvature. The bars, therefore, react differently to radial compressive forces applied thereto and also to forces tending to separate the collars, again for the purpose of providing a specific desired resistance characteristic.

The form in FIG. 8 utilizes non-bowed-type spring straps, as at 70, connecting collars 73 and 74 and having S-bends as at 72 which provide longitudinal resilience. Spring straps 70 function to resist axial separation of collars 73 and 74 and, thus, initially strengthen outer bow straps 71 against radial bending, as in the previous forms. As indicated above, maximum resistance to flexing would occur where bar 70 is constructed without substantial longitudinal resilience.

In each of the forms, by providing one or more spring members which have greater resistance to radial distortion or which are not exposed to direct radial bending forces, as indicated by the arrows 62 in FIG. 5, the resistance of the centralizer to radial compaction is greater than would be the case where the number of uniform straps engaging the bore wall is increased. Thus, a radially stiffer centralizer may be provided, in accordance with this invention, with the use of conventional bow spring strap material and without crowding the spaces between the straps and without providing a series of more-or-less conventional centralizers longitudinally aligned, as has been suggested.

The invention may be modified in various respects as will occur to those skilled in the art, and the exclusive use of all modifications as come within the scope of the appended claims is contemplated.

I claim:

1. In combination with a well, a centralizer for laterally positioning a pipe in the well without substantially restricting the flow of well fluid therepast comprising spaced, axially aligned collars for reception about the pipe and a plurality of outwardly bowed, arcuate spring strap members connecting and rigidly secured to said collars, some of said strap members engaging the surrounding well wall so as to resist approach of the pipe to said wall and longitudinal separation of said collars incidental thereto, at least another of said strap members being of different curvature than said first strap members so as to apply different resistance to longitudinal separation of said collars and thereby supplement the effective radial resilience of said first spring strap members.

2. A centralizer for laterally positioning an elongated device in an orifice comprising spaced, axially aligned uniform collars for slidable reception about the device and a plurality of outwardly bowed, arcuate spring strap members each connecting and rigidly secured to said collars, at least soem of said members extending to the radial limits of the centralizer for engaging a surrounding orificewall and resisting approach of the centralized device to said wall and longitudinal separation of said collars incidental thereto, others of said strap members being of different curvature than said first members so as to apply different resistance to longitudinal separation of said collars and thereby supplement the effective radial resilience of said first spring strap members.

3. A centralizer as described in claim 2 in which said second-mentioned strap members are of less radial expanse than said first members and subjected to longitudinal stressing during radial stressing of said first members.

4. A centralizer as described in claim 2 in which said other strap members are circumferentially interposed between pairs of said first members.

5. A centralizer as described in claim 2 in which each spring strap member of said first group is in radial and longitudinal alignment wwth one of said other strap members to form pairs of strap members in mutual prestressed relationship.

6. A centralizer as described in claim 2 in which said strap members are laterally resilient and include a first group extending radially beyond the others thereof for engaging the well wall and normally maintained in prestressed condition under longitudinal compression, said other strap members being longitudinally prestressed under tension.

7. A centralizer as described in claim 2 in which each of said other strap members is inside one of said first members and radially and longitudinally aligned therewith.

8. A centralizer as described in claim 7 further including spacer means interposed between the strap members of each radially and longitudinally aligned pair thereof.

9. A centralizer as described in claim 8 in which the strap members of said pairs are interr'nediately radially spaced apart and said spacer means extends only partially between said intermediate portions in the normal positions thereof.

10. A centralizer as described in claim 8 in which said spacer means is wedged between said strap member intermediate portions so as to initially stress said strap members.

1 1. A centralizer for well casing comprising a plurality of axially aligned and spaced collars adapted for slidable reception on the casing and radially stacked sets of bow spring members connecting said collars and projecting outwardly therefrom, the inner of said members being firmly secured at their ends to said collars so as to withstand heavy disaligning forces and dragging of the centralizer along a well bore in both directions by the enveloped casing.

12. A centralizer as described in claim 11 in which each of said sets comprises a plurality of bow springs rigidly secured together at their ends and to said collars and medially spaced apart.

13. In a well pipe centralizer having a pair of axially spaced and aligned collars adapted to slidably lit the well pipe and a plurality of circumferentially spaced and outwardly bowed spring staves extending longitudinally between and fixedly mounted on said collars, the improvement comprising: strap means extending longitudinally and having ends secured to the assembled staves and collars for imposing only a slight resistance to the initial inward deflection of said staves and substantially preventing the further axial separation of the collars for causing substantial resistance to inward deflection of said staves beyond a predetermined amount. a: 

1. In combination with a well, a centralizer for laterally positioning a pipe in the well without substantially restricting the flow of well fluid therepast comprising spaced, axially aligned collars for reception about the pipe and a plurality of outwardly bowed, arcuate spring strap members connecting and rigidly secured to said collars, some of said strap members engaging the surrounding well wall so as to resist approach of the pipe to said wall and longitudinal separation of said collars incidental thereto, at least another of said strap members being of different curvature than said first strap members so as to apply different resistance to longitudinal separation of said collars and thereby supplement the effective radial resilience of said first spring strap members.
 2. A centralizer for laterally positioning an elongated device in an orifice comprising spaced, axially aligned uniform collars for slidable reception about the device and a plurality of outwardly bowed, arcuate spring strap members each connecting and rigidly secured to said collars, at least soem of said members extending to the radial limits of the centralizer for engaging a surrounding orifice wall and resisting approach of the centralized device to said wall and longitudinal separation of said collars incidental thereto, others of said strap members being of different curvature than said first members so as to apply different resistance to longitudinal separation of said collars and thereby supplement the effective radial resilience of said first spring strap members.
 3. A centralizer as described in claim 2 in which said second-mentioned strap members are of less radial expanse than said first members and subjected to longitudinal stressing during radial stressing of said first members.
 4. A centralizer as described in claim 2 in which said other strap members are circumferentially interposed between pairs of said first members.
 5. A centralizer as described in claim 2 in which each spring strap member of said first group is in radial and longitudinal alignment wwth one of said other strap members to form pairs of strap members in mutual prestressed relationship.
 6. A centralizer as described in claim 2 in which said strap members are laterally resilient and include a first group extending radially beyond the others thereof for engaging the well wall and normally maintained in prestressed condition under longitudinal compression, said other strap members being longitudinally prestressed under tension.
 7. A centralizer as described in claim 2 in which each of said other strap members is inside one of said first members and radially and longitudinally aligned therewith.
 8. A centralizer as described in claim 7 further including spacer means interposed between the strap members of each radially and longitudinally aligned pair thereof.
 9. A centralizer as described in claim 8 in which the strap members of said pairs are intermediately radially spaced apart and said spacer means extends only partially between said intermediate portions in the normal positions thereof.
 10. A centralizer as described in claim 8 in which said spacer means is wedged between said strap member intermediate portions so as to initially stress said strap members.
 11. A centralizer for well casing comprising a plurality of axially aligned and spaced collars adapted for slidable reception on the casing and radially stacked sets of bow spring members connecting said collars and projecting outwardly therefrom, the inner of said members being firmly secured at their ends to said collars so as to withstand heavy disaligning forces and dragging of the centralizer along a well bore in both directions by the enveloped casing.
 12. A centralizer as described in claim 11 in which each of said sets comprises a plurality of bow springs rigidly secured together at their ends and to said collars and medially spaced apart.
 13. In a well pipe centralizer having a pair of axially spaced and aligned collars adapted to slidably fit the well pipe and a plurality of circumferentially spaced and outwardly bowed spring staves extending longitudinally between and fixedly mounted on said collars, the improvement comprising: strap means extending longitudinally and having ends secured to the assembled staves and collars for imposing only a slight resistance to the initial inward deflection of said staves and substantially preventing the further axial separation of the collars for causing substantial resistance to inward deflection of said staves beyond a predetermined amount. 